“Ridiculous” illegal reintroductions of rare or extinct butterflies to new sites in Britain risk introducing disease, damage attempts to save species and jeopardise well-planned releases, conservationists have warned.
Conservation scientists spoke out after black-veined whites, which fell extinct in Britain 100 years ago, reappeared on a nature reserve near Croydon.
Reintroductions of extinct species require licences from Natural England, the government’s conservation watchdog, and permission must also be sought to move rare protected butterflies to new sites.
Butterfly Conservation recently oversaw the successful reintroduction of the extinct chequered skipper to England with butterflies from Belgium but experts report “an outpouring” of unofficial releases of rare butterflies over the last five years.
Maverick breeders, heartened by public enthusiasm for rewilding and frustrated by the slow pace of restoration by mainstream conservation organisations, have released endangered marsh fritillaries and Glanville fritillaries on to dozens of new sites and also non-native species including the marbled fritillary. The breeders calculate that global heating makes Britain increasingly conducive to butterflies previously restricted to warmer countries.
“It is illegal to release an extinct species to Britain on to a Site of Special Scientific Interest (SSSI) with no disease control,” Dan Hoare, the conservation director of Butterfly Conservation, said of the return of the black-veined white. “There’s good scientific evidence that this could be not only ineffective but actively damaging. If you’re bringing in specimens from abroad you could be bringing in diseases. I would support someone being prosecuted for that.”
About 15 black-veined whites have been spotted at the London Wildlife Trust reserve of Hutchinson’s Bank, where in recent years endangered British species the Glanville fritillary, marsh fritillary and Duke of Burgundy have also suddenly appeared. Experts agree that the butterflies were highly unlikely to reach the site naturally and have been secretly put there by breeders.
“It’s just ridiculous – it’s become an outdoor zoo,” said Hoare of the site, which is popular with many butterfly enthusiasts hoping to see rare species.
Conservation scientists argue that unofficially introduced butterflies usually vanish again within several years. They say their release can put pressure on conservationists to manage a nature reserve to preserve that new species – actions that may be to the detriment of other rare invertebrates naturally found on the site.
Matthew Oates, a conservationist who has previously pointed out the positive contribution made by butterfly breeders, said the latest rogue releases had gone too far.
“I really feel for the conservation professionals who are trying to care for these sites. There’s been this outpouring of releases, particularly of Glanville fritillaries and marsh fritillaries. It’s stopping butterflies from speaking for themselves and masking our ability to measure natural spreads and contractions of their ranges.”
Moving more common butterflies such as the small blue on to new sites is not illegal if the breeder has permission from the landowner and the release site is not a protected area such as a SSSI.
Conservationist scientists say that rogue releases of native species risk undermining the diversity of butterfly subspecies in the country, potentially merging the genetic stock of different “ecotypes”, butterflies that have developed distinct habits or wing patterns in different regions. For instance, there are four subspecies of silver-studded blue in Britain.
Speaking on the condition of anonymity, a butterfly breeder said that there was an extinction crisis, conventional charities’ wildlife restoration was far too slow, and there was no evidence of accidentally introduced disease or “lethal genes” from releases damaging other butterfly or invertebrate populations.
The breeder, who has successfully returned hundreds of native butterflies to sites from where they had vanished, including the small blue and the purple emperor, said: “We can’t wait for Butterfly Conservation to pull their finger out. We’ve got to do something. It gives people a lot of joy too, which is why it has popular support.
“It’s wonderful if it works but if it doesn’t the introduced butterfly simply dies out. If it’s a species that isn’t in a particular area you won’t be introducing lethal genes because they won’t meet others of the same species. There are a lot of false arguments.”
Matthew Frith, of London Wildlife Trust, said it did not have the resources to investigate or prosecute rogue releases at Hutchinson’s Bank, nor did it wish to “add fuel to the fire” of a polarised debate.
But Frith said the multiple species introductions on the site had put them in “an awkward situation”.
“The whole credibility of the trust as a conservation organisation is being called into question,” he said. “We’re in a nature crisis. Do we relax some of the rules now because we’re running out of time? There is a debate to be had which is about looking at reducing some of the barriers to allow well-considered introductions.
“Hutchinson’s Bank is not managed as a butterfly garden but if through our management it supports a fantastic range of butterflies, that is to be celebrated.”
Delphine Pouget, the principal adviser for species reintroduction for Natural England, said: “Restoring lost species is an important and inspiring aspect of nature recovery, but it requires proper planning and execution to succeed and avoid any risks.
“For anyone interested in planning a conservation translocation project, they should align with Defra’s code and guidance for England on reintroduction and other conservation translocation.”
Reintroductions – official and “rogue”
Licensed
Large blue, Britain
Fell extinct in Britain in 1979, brought back to one site in Devon via caterpillars from Sweden. Took 30 years of conservation management before populations boomed and spread naturally; Britain now has the best population of the butterflies in Europe.
Chequered skipper, England
Extinct in England in 1977; adult butterflies collected in Belgium and returned to Northamptonshire woodland in 2018 by Butterfly Conservation. Population now in two sites.
Marsh fritillary, Cumbria
200 colonies dwindled to none by 2004. The last butterflies taken into captivity were found to be genetically very weak and so Scottish breeding stock was added to produce 42,000 larvae, released on to four sites. The butterfly is thriving again in Cumbria.
Rogue
Marsh fritillary, Chambers Farm Wood, Lincolnshire
Experts say the Marsh fritillary population released years ago by renowned breeder Martin White is genetically too narrow, requires intensive management to sustain it, and is too isolated to expand naturally.
Adonis blue, Devil’s Dyke, Cambridgeshire
Huge population flying there this year after a handful sighted in 2020. The butterfly could never reach this site by itself. The Chalkhill blue and small blue have also been successfully returned to East Anglia by unofficial releases.
Glanville fritillary, Weston-super-Mare
Unofficial release endured on the Somerset coast for some years from the 1990s but then died out. Critics say other unofficial Glanville releases on the mainland are doomed to fail – the species only survives naturally on the Isle of Wight because constant coastal erosion sustains its caterpillar’s foodplant.
